Blood Pressure Monitoring

SURGICAL CRITICAL CARE VIVAS B BLOOD PRESSURE MONITORING Define the blood pressure Blood pressure is defined as the product of the cardiac output and the systemic vascular resistance The cardiac output is the product of the heart rate and stroke volume Draw the blood pressure waveform mmHg BLOOD PRESSURE MONITORING In which ways can blood pressure be measured? Blood pressure can be measured non-invasively with a sphygmomanometer, or invasively by direct cannulation of a peripheral artery This latter method gives a continuous waveform trace after attachment to an electronic pressure transducer 120 80 Dicrotic notch Systolic Diastolic Arterial pressure waveform The ‘dicrotic notch’ is a momentary rise in the arterial pressure trace following closure of the aortic valve How is the mean blood pressure calculated? The area beneath the arterial pressure wave tracing represents the mean arterial pressure For the purposes of simplicity, it may be calculated by the formula Pd  (Ps  Pd)/3 where Pd diastolic pressure and Ps systolic pressure What is Allen’s test, and how is it performed? Allen’s test is a test of the competence of the collateral circulation of the hand – and may be used practically to determine 38 䉲 SURGICAL CRITICAL CARE VIVAS if the ulnar artery supply to the hand is able to cope in the face of an absent radial artery, e.g when considering the use of the radial artery as a vascular conduit for bypass surgery What are the complications of arterial lines, and what are the contra-indications to their insertion? The complications include 䊉 Most commonly: 䊏 Haematoma formation 䊏 Digital ischaemia due to vascular injury or accidental injection of drugs 䊉 Less commonly: 䊏 Infection 䊏 Pseudoaneurysm formation 䊏 Arteriovenous fistula formation 䊏 Exsanguination from a disconnected line It is contra-indicated in those with digital vasculitis, and in those patients who are going to have the artery of that side harvested as a conduit for bypass surgery BLOOD PRESSURE MONITORING The examiner occludes the blood f low to the hand while the patient drains the hand of blood by repeatedly opening and closing the fist The hand is then held open while the ulnar f low is released The test is considered positive if the hand is still blanched after 15 s, suggesting that the ulnar artery alone is not able to sufficiently supply the hand B What is meant by the term ‘swing in the arterial line’ during continuous measurements, and what is its significance? This term refers to a variation of the amplitude in the arterial tracing with the respiratory cycle It is an indicator that the patient is underfilled and requires more f luid resuscitation 䉲 39 SURGICAL CRITICAL CARE VIVAS B These differences are, in part, due to changes in wall stiffness along the arterial tree, and its consequent effects on the transmission of the pulse wave along the vessel 150 Ascending aorta 114 100 Pressure (mmHg) BLOOD PRESSURE MONITORING How does the arterial pressure at the radial artery compare to that at the aortic root, what accounts for this difference? Both the pressure values and waveform change at different levels of the circulation In the radial artery, the systolic pressure is about 10 mmHg higher and the diastolic pressure about 10 mmHg lower than in the aortic root Consequently, although the pulse pressure is higher in the radial artery, the mean arterial pressure is about mmHg lower than in the aortic root Mean 93 83 50 150 Radial Artery 100 50 126 Mean 89 71 Pressure waves at different sites in the arterial tree With transmission of the pressure wave into the distal aorta and large arteries, the systolic pressure increases and the diastolic pressure decreases, with a resultant heightening of the pulse pressure However, the mean arterial pressure declines steadily Adapted from "Circulatory Physiology" 3rd edition by Smith & Kampire p 93 Published by Williams & Wilkins ISBN 0683077759 40 䉲 SURGICAL CRITICAL CARE VIVAS What is pulsus paradoxus? Pulsus paradoxus is an exaggerated (
10 mmHg) reduction of the arterial pressure brought on by inspiration, and may be seen in cardiac tamponade The normal increase in the venous return brought on by inspiration coupled with a tight pericardial space leads to a reduction of the left ventricular end diastolic volume, and hence, stroke volume B BLOOD PRESSURE MONITORING How does the arterial pressure waveform differ with diseases of the aortic valve? 䊉 Aortic stenosis: Anacrotic pulse – slow to rise and of low amplitude 䊉 Aortic incompetence: Waterhammer pulse – rapid rise and decline, attaining high amplitude 䊉 Mixed aortic valve disease: Pulsus bisferiens – a large amplitude pulse with a ‘double peak’, often felt as a double pulse at the brachial artery What is pulsus alterans? Pulsus alterans is a random variation in the amplitude of the arterial pressure tracing with each cardiac cycle, and is seen with left ventricular failure 䊏 41 SURGICAL CRITICAL CARE VIVAS B BLOOD PRODUCTS BLOOD PRODUCTS What blood products you know of other than red cells? The other major blood products are 䊉 Plasma-derived 䊏 Fresh frozen plasma (FFP) 䊏 Human albumin solution 䊏 Immunoglobulins 䊏 Individual factor concentrates, e.g factors VII,VIII, IX, X, prothrombin complex, antithrombin III 䊏 Cryoprecipitate Note that FFP may be fractionated into the products listed below it 䊉 Platelet concentrates How are platelets stored once collected? Platelets not function at low temperatures, so that once collected, they are stored at room temperature of 20–24°C on a special agitator What is the shelf life of platelets? This is 5–7 days if sealed in special packaging that permits atmospheric oxygenation How many platelets are obtained from each donation? Each platelet donation contains 55  109 platelets When pooled together to form an adult dose, about 240  109 platelets can be obtained Give some indications for a platelet transfusion These are basically 䊉 Any cause of thrombocytopenia, when the count falls below 50  109/l 䊉 Note that the above includes disseminated intravascular coagulation 42 䉲 SURGICAL CRITICAL CARE VIVAS 䊉 Post cardiopulmonary bypass: It is known that this has a direct detrimental effect on platelet function Also, patients coming off bypass may still have a low body temperature, which reduces platelet function They may also have taken aspirin up to the time of surgery Platelets may in these instances be required to control bleeding even though the platelet count may not be that low BLOOD PRODUCTS What are the problems associated with platelet transfusion? 䊉 Risk of infection: as for a transfusion of packed red cells 䊉 Rhesus sensitisation: Rh negative females under the age of 45 should receive Rh-D negative platelets 䊉 Alloimmunisation: this is due to development of antibodies to HLA class I antigens It can lead to a febrile transfusion reaction and ‘refractoriness’ to therapy, when the platelet count rises less than expected following a transfusion B What are the two main components of FFP? The two main components are cryoprecipitate and cryosupernatant Taken together, they are a rich source of all of the clotting factors, von Willebrand factor, fibrinogen, and other plasma proteins How is FFP stored and what is the shelf life? FFP is stored at 30°C for up to 12 months Once thawed, it should be transfused immediately to prevent the loss of the labile factors V and VIII What is the dose of FFP? The dose of FFP is weight-dependent, and a typical starting dose is 10–15 ml/kg 䉲 43 SURGICAL CRITICAL CARE VIVAS B Give some indications for its (FFP) use 䊉 䊉 䊉 䊉 䊉 Reversal of warfarin effect Help control intra-operative/post-operative bleeding, e.g after cardiac surgery Following massive blood transfusion Disseminated intravascular coagulation Those with antithrombin III deficiency and resistance to heparinisation BLOOD PRODUCTS What components is cryoprecipitate particularly rich in? Cryoprecipitate is a rich source of fibrinogen, fibronectin, factors VIII, XIII (fibrin-stabilising factor), and von Willebrand factor What is the management of warfarin overdose? The management of warfarin overdose depends on the severity of the blood loss and the international normalised ratio (INR) 䊉 If the INR is
4.5 with no haemorrhage, the warfarin can be omitted for 1–2 days followed by a review 䊉 If haemorrhage is not severe, warfarin may again be omitted, and if indicated clinically, reversed with a slow i.v infusion of vitamin K, 0.5–2.0 mg 䊉 In the face of severe haemorrhage, mg of vitamin K is given by slow i.v infusion together with prothrombin complex concentrate (PCC), containing factors II, IX and X with factor VII Alternatively, FFP can be given, but may be less effective than PCC 䊉 These guidelines are based on the advice of the ‘Handbook of Transfusion Medicine’ published by Her Majesty’s Stationery Office (HMSO) What types of human albumin are available? Human albumin solution is available as either a 4.5% or 20% solution The latter is also known as ‘salt-poor albumin’ since it contains less sodium 44 䉲 SURGICAL CRITICAL CARE VIVAS B What is the use of this blood product? Some uses for human albumin 䊉 䊉 䊉 Management of ascites in portal hypertension Oedema due to other causes of hypoalbuminaemia such as the nephrotic syndrome As a plasma expander in hypovolaemic shock: there is no evident superiority over other colloids or crystalloids in this situation BLOOD PRODUCTS 䊏 45 SURGICAL CRITICAL CARE VIVAS B BLOOD TRANSFUSION What is the purpose of a blood transfusion? To restore the circulating volume in order to improve tissue perfusion and to maintain an adequate blood oxygen carrying capacity What is the volume of a unit of packed red cells? 280 60 ml BLOOD TRANSFUSION At what temperature is the blood stored? 2–6°C What is the shelf life of blood? 35 days, at the correct storage temperature What are the additive solutions and what is their purpose? The most common additive solutions are 䊉 CAPD: Citrate, Adenine, Phosphate, and Dextrose 䊉 SAMG: Saline, Adenine, Mannitol, and Glucose The additive solutions are used to re-suspend the packed cells after the plasma has been removed, and they maintain the cells in a good condition during storage What is the expected increase in the haemoglobin concentration [Hb] following a transfusion of packed red cells? A ml/kg dose of packed cells raises the [Hb] by g/dl What is the estimated blood volume in an adult and a child? The estimated blood volume in an adult is 70 ml/kg, in a child is 80 ml/kg 46 䉲 SURGICAL CRITICAL CARE VIVAS For which infections is donated blood screened? 䊉 Hepatitis B 䊉 Hepatitis C 䊉 HIV and 䊉 Syphilis In special circumstances, e.g for use in the immunocompromised, CMV is screened Define “massive transfusion” and what are the potential problems? A massive transfusion is defined as a transfusion equaling the patients’ blood volume within 24 h The potential problems are 䊉 Volume overload – can lead to acute pulmonary oedema in the susceptible 䊉 Thrombocytopenia: following storage there is a reduction of functioning platelets, so that there is a dilutional thrombocytopenia following a large transfusion 䊉 Coagulation factor deficiency – leading to a coagulopathy May require blood products such as FFP for reversal 䊉 Ineffective tissue oxygenation due to reduced of 2,3 bisphosphoglycerate, which does not store well 䊉 Hypothermia 䊉 䊉 BLOOD TRANSFUSION How may the complications of blood transfusion be classified? 䊉 Complications of massive transfusion 䊉 Complications of repeated transfusion 䊉 Infective complications 䊉 Immune reactions B Hypocalcaemia: Due to chelation by the citrate in the additive solution May compound the coagulation defect Hyperkalaemia: Due to progressive potassium leakage from the stored red cells 䉲 47 SURGICAL CRITICAL CARE VIVAS B Which coagulation factors are most affected by storage? The most labile of the coagulation factors are V and VIII The reduction of factor VIII may be offset by the metabolic response to stress, which stimulates factor VIII production BLOOD TRANSFUSION What infective complications may be seen following transfusion? 䊉 Hepatitis B and C 䊉 HIV 䊉 Syphilis 䊉 Yersinia enterocolitica: Gram negative organism often implicated in red cell transfusions 䊉 Gram positive infections, especially staphylococcal following contamination 䊉 Infections associated with endemic areas: Malaria, Chaga’s disease What would make you suspect that a unit of blood has bacterial contamination? 䊉 Presence of clots in the bag 䊉 High degree of haemolysed red cells Which immune reactions may occur following transfusion? Immune reactions seen are 䊉 Febrile reaction: Occurs within an hour of commencement as a reaction to white cell antigens in the donated blood 䊉 Acute haemolytic reaction following ABO-incompatibility This is usually due to a clerical error 䊉 Delayed haemolytic reaction: The patient is immunised to foreign red cell antigens due to previous exposure Can lead to jaundice and haemolysis days later 䊉 Post transfusion purpuric reaction: Occurs 7–10 days following transfusion due to reaction to platelet PIAI antigens 48 䉲 SURGICAL CRITICAL CARE VIVAS 䊉 䊉 Graft vs Host disease: A rare but almost-uniformly fatal reaction Immunocompetent donor lymphocytes mediate an immune reaction to the recipient Anaphylactic reaction B How is the risk of Graft vs Host disease reduced? This is prevented by irradiation of the sample, and not through the use of leukocyte-depleted blood Leukocyte depletion reduces the risk of CMV transmission BLOOD TRANSFUSION What are the signs and symptoms of an immediate haemolytic transfusion reaction? 䊉 Pyrexia and rigors 䊉 Headache 䊉 Abdominal and loin pain 䊉 Facial f lushing 䊉 Hypotension, progressing to acute renal failure, disseminated intravascular coagulation (DIC) and acute lung injury How is an immediate haemolytic transfusion reaction managed, and which investigations would you perform? 䊉 Stop the transfusion immediately 䊉 Commence i.v f luid resuscitation, ensuring that the urine output is greater than 30–40 ml/h 䊉 Repeat grouping on the pre- and post-transfusion recipient sample 䊉 Repeat the cross match 䊉 Perform a direct anti-globulin (Coomb’s test) on the recipient post-transfusion sample 䊉 Look for the presence of DIC – increased fibrindegradation products, coagulopathy 䊉 Check for evidence of the response to intravascular haemolysis – increased bilirubin, reduced circulating 䉲 49 SURGICAL CRITICAL CARE VIVAS B BLOOD TRANSFUSION 50 䊉 haptoglobins, haemoglobinaemia, and haemoglobinuria Monitor this for 24 h Send samples for blood culture in case this was, in fact, a septic episode in response to contaminated blood What is a direct Coomb’s test? Coomb’s test, also known as a direct antiglobulin test, is used for the detection of antibody or complement on the surface of red cells that have developed in vivo The indirect Coomb’s test detects red cell binding that has developed in vitro.The direct test can be used in the detection of cases of 䊉 Haemolytic transfusion reactions 䊉 Haemolytic disease of the newborn 䊉 Autoimmune haemolytic anaemias 䊏 SURGICAL CRITICAL CARE VIVAS B BRAINSTEM DEATH AND ORGAN DONATION What are the general criteria that must be met prior to donation? 䊉 The diagnosis of brainstem death must be established 䊉 The donor is maintained on a ventilator in the absence of untreated sepsis 䊉 There must not be a history of malignancy Primary brain tumours are exempt because of the confined nature of the disease 䊉 The donor must be HIV and hepatitis B negative 䊉 Those from high-risk groups, such as i.v drug abusers are excluded There is some variation on these requirements depending on the organ to be donated, such as no history of myocardial infarction for heart donors, and no history of alcohol abuse among liver donors Note that those with diabetes mellitus, smokers and those with hepatitis C are not immediately excluded BRAINSTEM DEATH AND ORGAN DONATION Which organs may be donated? 䊉 Kidneys 䊉 Heart 䊉 Lungs 䊉 Liver 䊉 Pancreas 䊉 Small bowel 䊉 Corneas 䊉 Skin 䊉 Bone and tendon Which law governs organ donation in the UK? In the UK, donation of human organs is managed under the control of the Human Tissue Act of 1961 䉲 51 SURGICAL CRITICAL CARE VIVAS B BRAINSTEM DEATH AND ORGAN DONATION Why is attention to fluid balance particularly important when optimising the physiology of the organ donor? Those with brainstem death develop rapidly diabetes insipidus following loss of posterior pituitary function This leads to free water loss, manifesting as a large urine output (
4 ml/kg/h), together with rising plasma osmolality and hypernatraemia It may be corrected temporarily with i.v dextrose In severe cases, management requires an infusion of arginine vasopressin to control urine output What other physiological changes may occur with brainstem death? 䊉 Development of hypothermia: following the loss of temperature regulation at the hypothalamic level This is exacerbated by reduced muscular and metabolic activity together with peripheral vasodilatation It is managed with the use of surface heating and warmed i.v f luids Note that hypothermia needs to be corrected before a diagnosis of brainstem death can be made correctly 䊉 Coagulopathy may result from hypothermia 䊉 Initial hypertension: due to an immediate increase in sympathetic activity This can lead to cardiovascular instability with arrhythmia formation 䊉 Hypotension soon follows due to the loss of sympathetic peripheral vascular tone This may require inotropic support of the mean arterial pressure and organ perfusion 䊉 Endocrine changes: following loss of anterior pituitary function The most important consequence is loss of thyroid hormone production, leading to further arrhythmias Triiodo-thyronine infusions have been used to help stabilise the patient in these situations Under which circumstances is it appropriate to perform an examination to confirm brainstem death? Clinical evaluation of the patient for the diagnosis of brainstem death must be justified, and so some preconditions must be met 52 䉲 SURGICAL CRITICAL CARE VIVAS The patient must be in a deep coma and reliant entirely on mechanical ventilation due to complete absence of spontaneous ventilation (‘apnoeic coma’) 䊉 There should be irreversible brain damage that is compatible with a diagnosis of brainstem death Those with the following, potentially reversible causes of coma should be identified and excluded 䊉 䊉 䊉 䊉 Drug and alcohol intoxication Endocrine disturbances: such as hypothyroidism, uraemic or hepatic encephalopathy Metabolic disturbances: such as hypoglycaemia, or sodium imbalance Hypothermia with a core temperature of 35°C What are the criteria for clinical confirmation of brainstem death? The tests involve both an evaluation of the brainstem ref lexes and the respiratory drive 䊉 Lack of respiratory drive following progressive hypercarbia: The subject is pre-oxygenated with 100% oxygen, and then disconnected from the ventilator for 10 while the PaCO2 is permitted to rise Normally, respiration is stimulated above a PaCO2 of 6.5 kPa 䊉 No brainstem function 䊏 Absent pupillary light ref lex 䊏 Absent corneal ref lex 䊏 Absent cranial nerve motor function 䊏 Absent gag and cough ref lex following pharyngeal and bronchial stimulation with a catheter 䊏 Absent vestibulo-ocular test following a cold caloric test The test should be repeated after an unspecified length of time for full confirmation BRAINSTEM DEATH AND ORGAN DONATION 䊉 B Who may legally perform these tests? The test must be performed by two clinicians who work in relevant areas of expertise, such as intensive care, anaesthesia, 䉲 53 SURGICAL CRITICAL CARE VIVAS B BRAINSTEM DEATH AND ORGAN DONATION 54 neurology or neurosurgery One of them should be a consultant, and the other must have been registered with the General Medical Council for at least five years They should not be part of the transplant team Under which clinical circumstances can confirmation prove difficult? 䊉 Chronic obstructive pulmonary disease 䊉 Eye injuries or pre-existing eye disease 䊉 Brain-stem encephalitis 䊏 SURGICAL CRITICAL CARE VIVAS B BRONCHIECTASIS What you understand by the term ‘bronchiectasis’? This is a localised or generalised irreversible dilatation of the bronchi arising as a result of a chronic necrotising infection It is classed as one of the obstructive airways diseases What is the aetiology of bronchiectasis? A number of disease processes lead to bronchiectasis, but the basic pathogenesis involves cycles of acute and chronic inf lammation accompanied by tissue damage and repair Some of the more common causes are 䊉 Bronchial obstruction: tumours, inhaled foreign body, extrinsic compression from lymphadenopathy 䊉 Infective processes: bacterial and viral pneumonias, e.g TB, measles, whooping cough, adenovirus 䊉 Mucociliary clearance defects: Kartagener’s and Young’s syndromes, cystic fibrosis 䊉 Primary and secondary immune deficiency states BRONCHIECTASIS What are the types of bronchiectasis? There are three overlapping pathologic forms of bronchiectasis 䊉 Follicular: characterised by the loss of bronchial elastic tissue and multiple lymphoid follicles 䊉 Atelectatic: a localised dilatation of the airways, associated with parenchymal collapse due to proximal airways obstruction 䊉 Saccular: which exhibits patchy dilatation of the airways In this situation, there is a loss of the normal bronchial subdivisions Which bacteria may colonise the airways in those with bronchiectasis? Bacterial colonisation often involve 䊉 Haemophilus influenzae 䊉 Streptococcus pneumoniae 䊉 Pseudomonas aeruginosa: in the chronically aff licted 䉲 55 SURGICAL CRITICAL CARE VIVAS B What complications can occur in the untreated patient with bronchiectasis? 䊉 In the short term: 䊏 Haemoptysis – which may be severe 䊏 Recurrent chest infections, lung abscess, empyema 䊏 Metastatic infection, e.g cerebral abscess 䊉 Long term: 䊏 Respiratory failure due to chronic airway obstruction 䊏 Cor pulmonale secondary to pulmonary hypertension 䊏 Secondary amyloidosis with protein A deposition BRONCHIECTASIS How is bronchiectasis managed? The principles of management involve 䊉 Management of reversible airway obstruction with bronchodilators and inhaled steroids 䊉 Physiotherapy to encourage expectoration of retained secretions Patients may also be trained to perform postural drainage techniques 䊉 Control of infection with antibiotics This depends on the organism isolated, but popular choices are cefaclor, ciprof loxacin or amoxycillin Prophylactic antibiotics have also been used 䊉 Management of the underlying causes, e.g airways obstruction, cystic fibrosis 䊉 Surgical intervention has also been used, such as lobectomy for localised disease In many instances, the disease is too diffuse to perform this Transplantation has also been used for complicated bronchiectasis 56 䊏 SURGICAL CRITICAL CARE VIVAS B BURNS How common are burn injuries in the UK? In the UK burns account for 10,000 hospital admissions and 600 deaths per annum What types of burns are there? Burns may be 䊉 Thermal: due to extreme heat or cold 䊉 Electrical 䊉 Chemical burns due to caustic substances BURNS What criteria may be used for the assessment of thermal burns? Burns are assessed by their extent on the body and their depth of skin penetration 䊉 Extent: described in terms of the percentage (%) body surface area covered As a rule of thumb, the area covered by the patients’ palm is equivalent to 1% Also by the ‘rule of nines’: anterior and posterior trunk 18%, head and arms 9%, legs 18% and genitalia 1% 䊉 Depth: may be superficial, partial or full-thickness: the clinical determinants of the depth are 䊏 Presence of erythema: seen in superficial burns 䊏 Blisters 䊏 Texture: leathery skin seen with full thickness burns 䊏 Sensation: burns are painful in areas where there is no full thickness penetration Why are burns patients susceptible to respiratory complications? 䊉 There may be a thermal injury to the nose or oropharynx with upper airway oedema 䊉 Smoke inhalation can lead to hypoxia with pulmonary oedema from ARDS 䉲 57 ... 114 100 Pressure (mmHg) BLOOD PRESSURE MONITORING How does the arterial pressure at the radial artery compare to that at the aortic root, what accounts for this difference? Both the pressure. .. harvested as a conduit for bypass surgery BLOOD PRESSURE MONITORING The examiner occludes the blood f low to the hand while the patient drains the hand of blood by repeatedly opening and closing... large arteries, the systolic pressure increases and the diastolic pressure decreases, with a resultant heightening of the pulse pressure However, the mean arterial pressure declines steadily Adapted